1. Field of the Invention
The present invention relates to a method of production of a spin valve type giant magnetoresistive thin film, and more particularly, relates to a method of production of a high performance spin valve type giant magnetoresistive thin film suitable for a magnetic recording head of a hard disk drive.
2. Description of the Related Art
A spin valve type giant magnetoresistive thin film used for a magnetic recording head of a hard disk drive has a multilayer film structure comprised of a plurality of layers (or thin films) including an antiferromagnetic layer, a fixed magnetization layer, a nonmagnetic conductive layer, and a free magnetization layer. In the multilayer film structure of the spin valve type giant magnetoresistive thin film, the nonmagnetic conductive layer is formed between the fixed magnetization layer and the free magnetization layer so that the two are isolated by the nonmagnetic conductive layer. Further, since the antiferromagnetic layer is made to adjoin the fixed magnetization layer, the magnetic moment of the fixed magnetization layer is fixed in one direction by the exchange coupling with the antiferromagnetic layer. On the other hand, the magnetic moment of the free magnetization layer is freely rotated in accordance with the external magnetic field.
The spin valve type giant magnetoresistive thin film generates the so-called xe2x80x9cgiant magnetoresistive effectxe2x80x9d, or the change of the electrical resistance due to the relative angle formed by the magnetic moment of the fixed magnetization layer and the magnetic moment of the free magnetization layer. The rate of change of the electrical resistance due to the giant magnetoresistive effect is called the xe2x80x9cmagnetoresistive ratioxe2x80x9d (MR ratio). The MR ratio of a spin valve type giant magnetoresistive thin film is far higher than that of a conventional anisotropic magnetoresistive thin film.
There are three types of spin valve type giant magnetoresistive thin films. The first type, as shown in FIG. 19, is a so-called xe2x80x9cbottom typexe2x80x9d comprised, from a substrate 111 side, of a buffer layer 112, an antiferromagnetic layer 113, a fixed magnetization layer 114, a nonmagnetic conductive layer 115, a free magnetization layer 116, and a protective layer 117 stacked consecutively in that order. The second type, as shown in FIG. 20, is a so-called xe2x80x9ctop typexe2x80x9d comprised, from a substrate 111 side, of a buffer layer 112, a free magnetization layer 116, a nonmagnetic conductive layer 115, a fixed magnetization layer 114, an antiferromagnetic layer 113, and a protective layer 117 stacked consecutively in that order. The third type, as shown in FIG. 21, is a so-called xe2x80x9cdual typexe2x80x9d comprised, from a substrate 111 side, of a buffer layer 112, a first antiferromagnetic layer 113A, a first fixed magnetization layer 114A, a first nonmagnetic conductive layer 115A, a free magnetization layer 116, a second nonmagnetic conductive layer 115B, a second fixed magnetization layer 114B, a second antiferromagnetic layer 113B, and a protective layer 117 stacked consecutively in that order.
In the above three types of spin valve type giant magnetoresistive thin films, in the past there have been proposed thin films replacing the single layers of the fixed magnetization layers 114, 114A, and 114B with synthtic ferrimagnet structures comprised of fixed magnetization layer elements, nonmagnetic layers, and fixed magnetization layer elements (U.S. Pat. No. 5,465,185). Further, the free magnetization layer 116 also comes in single layer structures and multilayer structures. In free magnetization layers and fixed magnetization layers of multilayer structures, all the layers are magnetic films, but sometimes different magnetic films are stacked or a sandwich structure interposing a nonmagnetic film therebetween is used.
The giant magnetoresistive effect of the above spin valve type giant magnetoresistive thin film is due to spin-dependent scattering of conductive electrons at the stacked interfaces of multilayer films. Therefore, to obtain a high MR ratio, cleanliness or flatness of the interfaces becomes important in the process of production of the spin valve film. Therefore, in the spin valve type giant magnetoresistive thin film, to achieve the cleanliness or flatness of the interfaces, the films are often formed continuously in the same vacuum chamber so that the intervals between formations of one layer and another become as short as possible.
Techniques for forming a film in vacuum include magnetron sputtering, ion beam sputtering, electron cyclotron resonance (ECR) sputtering, facing target sputtering, high frequency sputtering, electron beam evaporation, resistance heating evaporation, molecular beam epitaxy (MBE), etc.
To obtain a high MR ratio, the thickness of the nonmagnetic conductive layer 115 should be small so as to suppress the flow of conductive electrons not contributing to the giant magnetoresistive effect (shunt effect). If the thickness of the nonmagnetic conductive layer 115 is made small, however, the fixed magnetization layer 114 and the free magnetization layer 116 will end up coupling ferromagnetically through the nonmagnetic conductive layer 115. The interlayer coupling magnetic field (Hin) between the fixed magnetization layer and the free magnetization layer should be small for practical use of the magnetic recording head of a hard disk drive. A field of a value in the range of xe2x88x9210 to +10 Oe is preferable. In the past, to reduce the interlayer coupling magnetic field, the thickness of the nonmagnetic conductive layer 115 was set to a thick 2.5 to 3.5 nm.
Further, in the related art, the technique of reducing the ferromagnetic coupling occurring between the fixed magnetization layer and the free magnetization layer by inserting a nano oxide layer (NOL) of a size of not more than 1 nm into the fixed magnetization layer in the bottom type of spin valve film (Y. Kamiguchi et al.; Digests of INTERMAG ""99, DB-01) has been proposed. As a result, a relatively small interlayer coupling magnetic field is obtained and a high MR ratio is obtained even with a thin (2 to 2.5 nm) nonmagnetic conductive layer.
That is, in the conventional spin valve type giant magnetoresistive thin film, the thickness of the nonmagnetic conductive layer was set thick (2.5 to 3.5 nm) to reduce the interlayer coupling magnetic field, but the problem arose of a flow of conductive electrons not contributing to the giant magnetoresistive effect (shunt effect) and the MR ratio ending up being reduced. Further, in the process of production of the above nano oxide layer, an oxidation step becomes necessary in the middle of formation of the fixed magnetization layer. An oxidation step is complicated and is poor in reproducibility.
An object of the present invention is to provide a method of production of a spin valve type giant magnetoresistive thin film able to maintain a low interlayer coupling magnetic field and obtain a high MR ratio without the use of an oxidation step even when the nonmagnetic conductive layer is thin.
The method of production of the spin valve type giant magnetoresistive thin film according to the present invention is configured as follows in order to achieve the above object.
According to a first aspect of the present invention, there is provided a method of production of a spin valve type giant magnetoresistive thin film comprised of a buffer layer deposited on a substrate, a multilayer part comprised of a nonmagnetic conductive layer, a fixed magnetization layer and a free magnetization layer sandwiching this, and an antiferromagnetic layer formed adjoining the fixed magnetization layer, and a protective layer deposited at a topmost position, wherein at least one location in a plurality of interfaces formed between the nonmagnetic conductive layer and the buffer layer is treated by plasma. In the method of production of this spin valve type giant magnetoresistive thin film, a plurality of interfaces formed below the nonmagnetic conductive layer are suitably treated by plasma so as to enhance the flatness and cleanliness of the layers and thereby enable the high MR ratio and low interlayer coupling magnetic field (Hin).
Preferably, at the multilayer part, the fixed magnetization layer is formed at the substrate side, the free magnetization layer is formed at the protective layer side, the fixed magnetization layer and/or the free magnetization layer is comprised of a single layer or a plurality of layers, and at least one location in the plurality of interfaces formed between the nonmagnetic conductive layer and the buffer layer is treated by plasma. This method is a method of production of a bottom type of spin valve type giant magnetoresistive thin film.
Alternatively, at the multilayer part, the free magnetization layer is formed at the substrate side, the fixed magnetization layer is formed at the protective layer side, the fixed magnetization layer and/or the free magnetization layer is comprised of a single layer or a plurality of layers, and at least one location in any plurality of interfaces formed between the nonmagnetic conductive layer and the buffer layer and any plurality of interfaces in the fixed magnetization layer is treated by plasma. This method is a method of production of a top type of spin valve type giant magnetoresistive thin film.
Alternatively, at the multilayer part, the fixed magnetization layer includes a bottom fixed magnetization layer and a top fixed magnetization layer, the nonmagnetic conductive layer includes a bottom nonmagnetic conductive layer and a top nonmagnetic conductive layer, a five-layer structure is formed based on the bottom fixed magnetization layer and free magnetization layer sandwiching the bottom nonmagnetic conductive layer and the free magnetization layer and top fixed magnetization layer sandwiching the top nonmagnetic conductive layer, at least one layer of the bottom fixed magnetization layer, the top fixed magnetization layer, and the free magnetization layer is comprised of a single layer or a plurality of layers, and at least one location in any plurality of interfaces formed between the bottom nonmagnetic conductive layer and the buffer layer and any plurality of interfaces between the top nonmagnetic conductive layer and free magnetization layer is treated by plasma. This method is a method of production of a dual type of spin valve type giant magnetoresistive thin film.
According to a second aspect of the invention, there is provided a method of production of a bottom type of spin valve type giant magnetoresistive thin film comprised of a buffer layer, an antiferromagnetic layer, a fixed magnetization layer, a nonmagnetic conductive layer, a free magnetization layer, and a protective layer consecutively stacked in that order on a substrate, wherein at least one location in the interface between the buffer layer and the antiferromagnetic layer, the interface between the antiferromagnetic layer and the fixed magnetization layer, and the interface between the fixed magnetization layer and the nonmagnetic conductive layer is treated by plasma.
Preferably, the fixed magnetization layer is a synthtic ferrimagnet type fixed magnetization layer having a three-layer structure of a first fixed magnetization layer element and a second fixed magnetization layer element isolated by a nonmagnetic layer, and at least one location in the interface between the antiferromagnetic layer and first fixed magnetization layer element, the interface between the first fixed magnetization layer element and nonmagnetic layer, the interface between the nonmagnetic layer and the second fixed magnetization layer element, and the interface between the second fixed magnetization layer element and the nonmagnetic conductive layer is treated by plasma.
According to a third aspect of the invention, there is provided a method of production of a top type of spin valve type giant magnetoresistive thin film comprised of a buffer layer, a free magnetization layer, a nonmagnetic conductive layer, a fixed magnetization layer, an antiferromagnetic layer, and a protective layer consecutively stacked in that order on a substrate, wherein at least one location in the interface between the buffer layer and the free magnetization layer and the interface between the free magnetization layer and the nonmagnetic conductive layer is treated by plasma.
Preferably, the fixed magnetization layer is a synthtic ferrimagnet type fixed magnetization layer having a three-layer structure of a first fixed magnetization layer element and a second fixed magnetization layer element isolated by a nonmagnetic layer, and at least one location in the interface between the first fixed magnetization layer element and the nonmagnetic layer and the interface between the nonmagnetic layer and the second fixed magnetization layer element is treated by plasma.
According to a fourth aspect of the invention, there is provided a method of production of a dual type of spin valve type giant magnetoresistive thin film comprised of a buffer layer, a first antiferromagnetic layer, a first fixed magnetization layer, a first nonmagnetic conductive layer, a free magnetization layer, a second nonmagnetic conductive layer, a second fixed magnetization layer, a second antiferromagnetic layer, and a protective layer consecutively stacked in that order on a substrate, wherein at least one location in the interface between the buffer layer and the first antiferromagnetic layer, the interface between the first antiferromagnetic layer and the first fixed magnetization layer, the interface between the first fixed magnetization layer and the first nonmagnetic conductive layer, and the interface between the free magnetization layer and the second nonmagnetic conductive layer is treated by plasma.
Preferably, the first fixed magnetization layer is a first synthtic ferrimagnet structure comprised of a three-layer structure of a first fixed magnetization layer element, a first nonmagnetic layer, and a second fixed magnetization layer element; the second fixed magnetization layer is a second synthtic ferrimagnet structure comprised of a three-layer structure of a third fixed magnetization layer element, second nonmagnetic layer, and fourth fixed magnetization layer element; and at least one location in the interface between the first antiferromagnetic layer and first fixed magnetization layer element, the interface between the first fixed magnetization layer element and first magnetic layer, the interface between the first nonmagnetic layer and second fixed magnetization layer element, the interface between the second fixed magnetization layer element and first nonmagnetic conductive layer, the interface between the third fixed magnetization layer element and second nonmagnetic layer, and the interface between the second nonmagnetic layer and fourth fixed magnetization layer element is treated by plasma.
In each of the above aspects of the invention, preferably the buffer layer is a multilayer film comprised of at least two types of layers, and at least one location in any plurality of interfaces existing in the buffer layer is treated by plasma.
In each of the above aspects of the invention, preferably the plasma treatment uses plasma using a 13.56 MHz RF wave in a gas atmosphere of any of 0.01 to 100 Pa low pressure inert gas of Ar, Kr, Xe, Ne, or gas resembling the same and the electrode structure is a type of parallel plate and capacitively-coupled.
In each of the above aspects of the invention, preferably, in the electrode structure, a substrate to be treated by plasma is arranged on an electrode provided with the RF wave, the power by the RF wave is not more than 0.5 W/cm2 per unit area, and a bias voltage applied to the substrate is in a range of less than 0V and at least xe2x88x92300V. Further, in each of the above aspects of the invention, preferably the treatment time of the plasma treatment is a time not more than one minute.
In each of the above aspects of the invention, preferably the plasma treatment is performed using ion bombardment (ion beam irradiation) based on an ion irradiation structure.
According to the method of production of a spin valve type giant magnetoresistive thin film according to the present invention, the formation of the spin valve film for forming the multilayer structure is temporarily interrupted during the formation, interfaces are treated by the ion bombardment, preferably plasma treatment, then the formation of the film is resumed. With this method of production, the plasma treatment does not necessarily have to be performed in a film forming chamber. It may also be performed after moving to an adjoining vacuum chamber of another vacuum chamber through a vacuum transport chamber etc.
Further, according to the method of production of the present invention, regardless of the structure of the spin valve film such as the bottom type, top type, or dual type, when using a Cu layer for the nonmagnetic conductive layer and setting the thickness of the Cu layer to 2.1 nm, the interfaces for plasma treatment etc. are suitably selected in accordance with the bottom type, top type, or dual type of spin valve film structure so that the interlayer coupling magnetic field (Hin) between the fixed magnetization layer and the free magnetization layer through the Cu layer becomes the smallest and the MR ratio becomes the largest. Further, the interruption of the film formation by the plasma treatment is not necessarily limited to one instance. It may be performed a plurality of times in accordance with need.
Further, according to the method of production of the present invention, depending on the material used for the layer to be treated by plasma, the conditions (RF power, treatment time, pressure of Ar etc., etc.) are changed so that the interlayer coupling magnetic field Hin becomes smaller and the MR ratio becomes larger. Further, in the method of production according to the present invention, no process using oxygen or oxidation step is used at all.